glide2x djgpp build fixes #6/7:

h3, dos_mode.c: add missing includes.

glide2x/h3/minihwc/dos_mode.c

@@ -34,9 +34,17 @@
 #include <string.h>
 
 #include <3dfx.h>
+#define FX_DLL_DEFINITION
+#include <fxdll.h>
+#ifdef __DJGPP__
+#include <dos.h>
+#else
 #include <i86.h>
+#endif
 #include <gdebug.h>
 
+#include <h3cinit.h>
+
 static FxU16 oldVidMode;
 
 typedef struct {